The invention relates to lubricant compositions having antimicrobial properties and to methods for manufacturing and using lubricant compositions having antimicrobial properties. The lubricant compositions are particularly useful for lubricating food handling/processing machinery commonly used in the food processing industry.
Oil-based lubricants are commonly used in the food processing industry in order to provide lubrication in gear boxes, pumps, hydraulic systems, agitators, grinders, etc. Although the lubricant is often provided inside a piece of machinery which is generally isolated from the exterior environment, food processing equipment is often cleaned using a high pressure water stream. Over time, water from cleaning operations tends to make its way into the machinery and contact the lubricant, forming a water and oil emulsion. Such water and oil emulsions become fertile grounds for growth of bacteria, yeast, and molds.
A food grade lubricant is available under the name No-Tox(copyright) from Bel-Ray Company, Inc. The lubricant incorporates an antimicrobial agent. Another lubricant containing a bacteriostatic agent is available under the name Lubristat(copyright) from Whitmore Mfg., Inc.
Lubricants containing antimicrobial agents are disclosed U.S. Pat. No. 3,826,746 to Schiek, et al. In general, Schiek, et al. describes lubricant compositions, such as, petroleum lubricant compositions, containing biocidal agents as microbial inhibitors. The biocidal agents include a substituted nitropyridine and an acid. In general, the concern is that bacteria may metabolize the hydrocarbons and result in the formation of deleterious metabolites.
A lubricant composition is provided by the invention. The lubricant composition includes a machinery lubricant and an antimicrobially effective amount of an antimicrobial agent exhibiting a partition coefficient between water and the machinery lubricant of between about 0.01 and about 1,000. The partition coefficient is the ratio of the weight fraction of the antimicrobial agent in water relative to the weight fraction of the antimicrobial agent in oil, wherein the ratio is determined at equilibrium. In addition, the lubricant composition exhibits at least a two log reduction of bacteria in water in about two weeks and/or at least a two log reduction of mold and yeast in water in about one month from a concentration of bacteria of between 105 and 106 CFU/ml (colony forming units/ml) and a mold and yeast concentration of between 105 and 106 CFU/ml.
A method for manufacturing a lubricant composition is provided by the invention. The method includes a step of mixing machinery lubricant and an antimicrobially effective amount of an antimicrobial agent exhibiting a partition coefficient between water and the machinery lubricant of about 0.01 and about 1,000.
A method for using a lubricant composition in machinery is provided by the invention. The method includes a step of introducing a lubricant composition containing a machinery lubricant and an effective amount of an antimicrobial agent, into machinery to provide lubrication properties. Exemplary machinery includes gear boxes, pumps, hydraulic systems, agitators, and grinders. The lubricant composition can be used in environments where microbial contamination is a concern. Exemplary environments include food processing equipment, pharmaceutical processing equipment and cosmetic processing equipment.
The invention relates to a lubricant composition containing a machinery lubricant and an antimicrobially effective amount of an antimicrobial agent. Machinery lubricants are commonly available. Machinery lubricants which can be used according to the invention include petroleum derived lubricants. A preferred type of machinery lubricant which can be used to provide the lubricant composition according to the invention is a food machinery lubricant. In general, food machinery lubricants include those lubricants which can be used on food processing machinery in the food processing industry where there is a possibility of incidental contact with food. In general, such lubricants do not include large amounts of impurities harmful to humans. Lubricants which can be used on food processing equipment include FDA-approved food grade lubricants. Machinery lubricants can include oils and/or greases.
Various food grade oils and greases are commercially available. In general, types of food grade oils which can be used according to the invention include paraffinic oils, synthetic polyalpha olefin oils, aluminum complex grease, and mineral oil. Exemplary food machinery lubricants which can be used according to the invention are available from Vulcan Oil and Chemical Products of Cincinnati, Ohio under the names Ariadne(trademark), Athena(trademark), Bacchus(trademark), Hercules(trademark), Olympus(trademark), Posseidon(trademark), Zeus(trademark), Prestige(trademark), and Ep Grease(trademark).
The antimicrobial agents which can be incorporated into the machinery lubricants to provide an antimicrobial effect include those antimicrobial agents which function to kill bacteria and/or yeast and mold which may exist in the machinery lubricant or become introduced into the machinery lubricant. Preferred antimicrobial agents include those which can be accepted for use on machinery in the food processing industry. In general, antimicrobial agents which are considered toxic to humans at levels needed to provide antimicrobial effect are not preferred antimicrobial agents for use in the food processing industry. Additional industries in which it is desirable to provide a machinery lubricant containing an antimicrobially effective amount of an antimicrobial agent include pharmaceutical processing and cosmetic processing.
The antimicrobial agents which can be incorporated into the machinery lubricants according to the invention are those exhibiting a distribution coefficient between water and the machinery lubricant which is sufficient to allow it to function as an antimicrobial agent over the life of the lubricant composition on a particular piece of machinery. The applicants discovered the desirability of providing an antimicrobial agent which exhibits solubility in both oil and water phases. As a result, when water is introduced into the lubricant composition, a portion of the antimicrobial agent provided in the oil phase becomes solubilized in the water phase. If the solubility of the antimicrobial agent in the oil phase is too high relative to its solubility in the water phase, a sufficient amount of antimicrobial agent to kill microbes in the water phase may not move into the water phase. In addition, if the antimicrobial agent is too water soluble relative to its oil solubility, too much antimicrobial agent may move into the water phase depleting the oil phase of antimicrobial agent and thereby reducing the longevity or life of the lubricant composition as an antimicrobial composition. That is, the lubricant composition may lose its effectiveness as an antimicrobial composition too quickly. A property which reflects the competitive solubility between the oil phase and the water phase can be referred to as the distribution coefficient. The distribution coefficient is generally expressed as a ratio of the weight fraction of the antimicrobial agent in water relative to the weight fraction of the antimicrobial agent in oil, wherein the ratio is determined at equilibrium. Preferably, the distribution coefficient for an antimicrobial agent in a lubricant composition is between about 0.01 and about 1,000. It is pointed out that a high distribution coefficient of about 1,000 may be considered acceptable if there is very little water contacting the lubricant composition and/or if the lubricant composition is replaced fairly frequently. A preferred distribution coefficient is between about 0.1 and about 100, more preferably between about 0.2 and about 50, and more preferably between about 0.5 and 20. In general, the distribution coefficient can be determined by varying the amounts of oil, water, and antimicrobial agent and running a regression of the data. The water, oil, and antimicrobial agent composition is preferably agitated and allowed to phase separate. Once an equilibrium is reached, the amount of antimicrobial agent in the water phase or oil phase or both can be measured. A technique for measuring the weight percent of an antimicrobial agent in water includes high performance liquid chromatography (HPLC).
Exemplary classes of antimicrobial agents which can be used according to the invention include substituted phenolics, polyhalides, interhalides, iodophores, percarboxylic acids, carboxylic acids, quaternary compounds and mixtures thereof. The antimicrobial agents can be provided in the lubricant composition at a concentration of between about 0.001 wt. % and about 10 wt. %.
Substituted phenolic antimicrobial agents includes esters of parahydroxy benzoic acids. Preferred esters of parahydroxy benzoic acid include alkyl esters of parahydroxy benzoic acid. Preferred alkyl groups include C1 to C8 alkyl groups, and more preferably C1 to C4 alkyl groups. Preferred esters of parahydroxy benzoic acid include the methyl, ethyl, propyl, and butyl esters. Preferred antimicrobial agents of this type are available under the name paraben. A preferred paraben compound includes methyl paraben (methyl 4-hydroxybenzoate). Esters of parahydroxy benzoic acid can include those esters of parahydroxy benzoic acid other than methyl paraben. Additional paraben compounds which can be used include ethyl paraben, propyl paraben, and butyl paraben. In general, the esters of parahydroxy benzoic acid are provided in an amount to provide an antimicrobial effect. In general, this corresponds with an amount of at least about 100 ppm based on the weight of the lubricant composition. Preferably, the amount is between about 500 ppm and about 5,000 ppm based on the weight of the lubricant composition.
Additional substituted phenolic antimicrobial agents include hydroxy anisole compounds, hydroquinone compounds, and hydroxytoluene compounds. A preferred hydroxy anisole compound is 2-butylated hydroxy anisole (BHA). A preferred hydroquinone compound is tertiary butylhydroquinone (TBHQ). A preferred hydroxytoluene compound is butylated hydroxytoluene (BHT). The hydroxy anisole compounds, hydroquinone compounds, and hydroxytoluene compounds are preferably used in an amount of between about 500 ppm and about 2,000 ppm based on the weight of the lubricant composition
Polyhalide antimicrobial agents which can be used according to the invention include substituted ammonium. Preferred polyhalides have the following formula: 
wherein R, Rxe2x80x2, Rxe2x80x3, and Rxe2x80x2xe2x80x3 may be the same or different and independently are a straight or branched, unsaturated or saturated, hydrocarbon group of 1 to 24 carbon atoms, in which the hydrocarbon chain is unsubstituted or substituted by hydroxyl, carboxyl, or alkylamido, or in which the hydrocarbon chain is uninterrupted or interrupted by a heteroatom; an aryl group, or aralkyl group in which alkyl has 1 to 4 carbon atoms. A is a counter ion which may be, for example, sulfate, methyl sulfate, and acetate. V is 0 to 1, W is 0 to 4, X is 0 to 7, Y is 0 to 9, and Z is 0 to 1 wherein V+W+X+Y+Z is at least 2, and more preferably wherein W+X+Y+Z is at least 2. Preferably, Y is 1 to 5.
Preferred quaternary nitrogen compounds that can be used to prepare polyhalides include quaternary ammonium compounds having the formula: 
wherein X is an anion except a hydroperoxide anion and R, Rxe2x80x2, Rxe2x80x3 and Rxe2x80x2xe2x80x3 are each independently a straight or branched, unsaturated or saturated, hydrocarbon group of 1 to 24 carbon atoms, in which the hydrocarbon chain is unsubstituted or substituted by hydroxyl, carboxyl, or alkylamido, or in which the hydrocarbon chain is uninterrupted or interrupted by a heteroatom; an aryl group, or aralkyl group in which alkyl has 1 to 4 carbon atoms. One embodiment of the formula I includes a compound where Rxe2x80x2 is benzyl and Rxe2x80x3 is aryl or benzyl.
An alkyl group is defmed as a paraffmic hydrocarbon group which is derived from an alkane by removing one hydrogen from the formula. The hydrocarbon group may be linear or branched. Simple examples include methyl (CH3) and ethyl (C2H5). However, in the present invention, at least one alkyl group may be medium or long chain having, for example, 8 to 16 carbon atoms, preferably 12 to 16 carbon atoms.
An alkylamido group is defined as an alkyl group containing an amide functional group: xe2x80x94CONH2, xe2x80x94CONHR, xe2x80x94CONRRxe2x80x2.
A heteroatom is defined as a non-carbon atom which interrupts a carbon chain. Typical heteroatoms include nitrogen, oxygen, phosphorus, and sulfur.
An aryl group is defined as a phenyl, benzyl, or naphthyl group containing 6 to 14 carbon atoms and in which the aromatic ring on the phenyl, benzyl or naphthyl group may be substituted with a C1-C3 alkyl. An aralkyl group is aryl having an alkyl group of 1 to 4 carbon atoms.
Certain quaternary nitrogen compounds are especially preferred. These include alkyl trimethyl ammonium salts, dialkyl dimethyl ammonium salts, alkyl dimethyl piperidinium salts, and alkyl dimethyl pyridinium salts.
Several preferred compounds are shown below. The first structure shown is cetyl trimethyl ammonium chloride; the second structure is didecyl dimethyl ammonium chloride; and the third is choline chloride. Another source of choline is available from phosphatidyl choline which is commercially available in lecithins. 
In each structure, the ammonium nitrogen is seen as covalently bonded to four substituents and ionically bonded to a chlorine anion.
The nitrogen compound can also be a protonated amine of the formula: 
wherein X1 is an anion; and R10, R11 and R12 are each, independently, hydrogen or at least one straight or branched, saturated or unsaturated, hydrocarbon group of 1 to 24 carbon atoms, in which the hydrocarbon chain is unsubstituted or substituted by hydroxyl, carboxyl, or alkylamido, or in which the hydrocarbon chain is uninterrupted or interrupted by a heteroatom; an aryl group, or aralkyl group in which alkyl has 1 to 4 carbon atoms.
In the invention, the quaternary ammonium cation can also be generated from an amphoteric molecule. An amphoteric compound can function as either an acid or as a base, depending on its environment, and has both functional groups present. A representative structure of the cation generated from an amphoteric molecule is shown below: 
wherein W is a linear or branched alkylene, hydroxyalkylene or alkoxyalkylene group having 1-6 carbon atoms;
Rb is R4xe2x80x94COxe2x80x94NH in which R4 is a saturated or unsaturated, branched or linear hydrocarbon group having 4-22 carbon atoms, or R4;
R1 is hydrogen, A or (A)nxe2x80x94Wxe2x80x94CO2xe2x88x92M+ in which A is a linear or branched alkyl, hydroxyalkyl or alkoxyalkyl having 1-4 carbon atoms, n is an integer from 0 to 6, and M is an alkali metal cation, a hydrogen ion or an ammonium cation;
R2 is (A)nxe2x80x94Wxe2x80x94CO2xe2x88x92M+;
R3 is hydrogen or A; and
X is an anion.
An example of a suitable amphoteric is shown below: 
where R is hydrogen, straight or branched alkyl having 1 to 16 carbon atoms, in which the alkyl group is uninterrupted or interrupted by phenyl. This is not itself a quaternary ammonium compound. Treatment with an organic or inorganic acid H+Xxe2x88x92 can result in a compound of the formula: 
where Xxe2x88x92 is an anion. This does indeed represent a quaternary ammonium compound which can be mixed with an appropriate oxidant and halogen, or halide salt, to meet the claimed invention, wherein.
Another class of amphoteric compounds can include the phosphorus containing species such as phospholipids like the lecithins (including phosphatidyl choline.), sphingomyelin, and the cephalins. Or modified phospho-amphoterics such as the Phosphoterics(copyright), sold by Mona Industries.
The invention can also use protonizable nitrogen sources. Examples include proteins, amino acids, amine oxides and amines which can form acid salts and mixtures thereof. These include, for example, sarcosine, taurine, glycine, and simple proteins such as albumins, phosphoproteins, protamines, histones, chromoproteins, schleroproteins, glutenins and globulins. Examples of protonizable proteins include milk, egg, blood and plant proteins. The nitrogen compound can be a protein, an acid salt thereof, or a mixture of proteins and their corresponding acid salts. Generally, these can be characterized as: 
wherein Ra is a linear or branched, saturated or unsaturated, hydrocarbon, hydroxyalkyl or alkoxyalkyl group having 1-22 carbon atoms; Rb is H or CH3, and W is a linear or branched alkylene, hydroxyalkylene or alkoxyalkylene group having 1-4 carbon atoms.
Rd is a common moiety as part of natural amino acids; e.g., H, alkyl, hydroxyalkyl, thioalkyl, alkyl-aryl, carboxyl, amido, alkyl-amino, and the like.
[poly-peptide]acidified+ refers to an acidified polypeptide, such as an acidified protein.
Additional preferred quaternary nitrogen sources include a choline, particularly a choline chloride, a choline bitartrate, an acetyl choline; or mixtures thereof. An additional preferred compound is cetyl dimethyl pyridinium chloride. The nitrogen source may also include mixtures thereof.
The nitrogen compound can also be a betaine, sultaine or phosphobetaine of the formula 
wherein Z is CO2H, CO2xe2x88x92, SO3H, SO3xe2x88x92, OSO3H, OSO3xe2x88x92, OPO3H or OPO3xe2x88x92; W is a linear or branched alkylene, hydroxyalkylene or alkoxyalkylene group having 1-6 carbon atoms; and
Ra is a linear or branched alkyl, hydroxyalkyl or alkoxyalkyl group having 1-22 carbon atoms; or R4xe2x80x94COxe2x80x94NH(CH2)x, in which R4 is a saturated or unsaturated, branched or linear hydrocarbon group having 4-22 carbon atoms, and xxe2x80x2 is an alkylene group having 1-6 carbon atoms.
A suitable betaine cation is shown below: 
wherein; R is a linear or branched alkyl, hydroxyalkyl or alkoxyalkyl group having 1-22 carbon atoms; or R4xe2x80x94COxe2x80x94NH(CH)x in which R4 is a saturated or unsaturated, branched or linear hydrocarbon group having 4-22 carbon atoms, and x is an alkylene group having 1-6 carbon atoms. Of special interest is the natural product betaine where R has 1 carbon atom.
In another embodiment, the nitrogen compound can be of the formula: 
wherein R6, R7 and R8 are each, independently, H or xe2x80x94A1xe2x80x94Y in which A1 is a C7 to C20 saturated or unsaturated, linear or branched alkylene group, and Y is H, NH2, OH or COOM1 in which M1 is H or a Group I metal ion;
B is a C1 to C20 saturated or unsaturated, linear or branched chain alkylene group, and Y1 is H, NH2, OH, COOM2 or xe2x80x94NHxe2x80x94CORq in which M2 is H or a Group I metal ion and Rq is a C1 to C20 saturated or unsaturated, linear or branched chain alkyl group;
R5 is H or a C1 to C3 alkyl group at one of the nitrogen atoms; and
X1 xe2x88x92 is an anion.
Typical imidazolines are: coconut hydroxyethyl imidazoline, tall oil aminoethyl imidazoline, oleyl hydroxyethyl imidazoline, the Miramines(copyright), the Rhodaquats(copyright), the Monazolines(copyright), the Rewoterics(copyright), the Crodazoline(copyright), available from Mona Industries Inc., Rhone Poulenc, Rewo Chemische Werke GmbH, and Croda Surfactants Ltd.
Exemplary quaternary ammonium compounds include those described in U.S. application Ser. No. 09/277,592, filed Mar. 26, 1999, the entire disclosure of which is incorporated herein by reference.
The amount of polyhalide antimicrobial agent provided in the lubricant composition is preferably at least about 10 ppm based on the weight of the lubricant composition. In general, the amount of polyhalide antimicrobial agent provided in the lubricant composition is less than about 10,000 ppm or 1 wt. %.
Interhalides which can be used as antimicrobial agents according to the invention include iodine monochloride (ICl) and iodine dichloride (ICl2xe2x88x92). Interhalides are generally useful as antimicrobial agents in the lubricant composition at a concentration of at least about 10 ppm. Preferably, the amount of interhalide is provided at less than about 10,000 ppm or 1 wt. %.
Iodophores which can be used as antimicrobial agents according to the invention include iodine complexes of nonionic surfactants and iodine complexes of polyvinylpyrrolidone. In addition, molecular iodine can be used as an antimicrobial agent. Iodophores and/or molecular iodine are preferably provided at a concentration of at least about 10 ppm, and preferably at a concentration of between about 10 ppm and about 10,000 ppm or 1 wt. %.
Percarboxylic acid antimicrobial agents which can be used according to the invention include C2 to C18 percarboxylic acids including peracetic acid, peroctanoic acid, pemonanoic acid, and perdecanoic acid. In addition, dipercarboxylic acids can be used such as persuccinic acid, perglutaric acid, permaleic acid, perfumaric acid, peradiptic acid, and mixtures thereof. In general, the amount of peracid antimicrobial agent is preferably between about 10 ppm and about 10,000 ppm based on the weight of the lubricant composition.
Carboxylic acids which can be used as antimicrobial agents according to the invention include C1 to C11 aliphatic and aromatic carboxylic acids and/or the salts of C1 to C11 aliphatic and aromatic carboxylic acids. Preferred carboxylic acids include butyric acid, heptanoic acid, octanoic acid, nonanoic acid, decanoic acid, benzoic acid, sorbic acid, salicic acid, ethyl-hexanoic acid, lactic acid, and mixtures thereof. The carboxylic acids are preferably provided at a concentration of at least about 10 ppm, and more preferably between about 10 ppm and about 10,000 ppm or 1 wt. %.
Quaternary compounds which can be used as antimicrobial agents according to the invention include quaternary ammonium and quaternary phosphonium compounds. Preferably, the concentration of quaternary compounds provided in the lubricant composition is at least about 100 ppm. Preferably, the concentration of quaternary compounds in the lubricant composition is less than about 5,000 ppm.
Preferred quaternary ammonium compounds include dioctyldimethyl ammonium chloride, didecyl dimethyl ammonium chloride, octyldecyl dimethyl ammonium chloride, tetramethyl ammonium chloride, alkyl dimethyl benzyl ammonium chloride (preferably, the alkyl group contains between about C6 to about C18 carbon atoms), didodecyldimethyl ammonium chloride, cetyltrimethyl ammonium bromide, benzyloctadecyldimethyl ammonium chloride, and dodecyldimethyl (2-phenoxyethyl) ammonium bromide.
Further exemplary quaternary ammonium compounds include benzalkonium chlorides, substituted benzalkonium chlorides, cetylpyridinium chloride, N-(3-chloroallyl) hexaminium chloride, domiphen bromide, benzethonium chloride, and methylbenzethonium chloride. Monoalkyltrimethyl ammonium salts include cetyltrimethyl ammonium bromide, alkyltrimethyl ammonium chloride, alkylaryltrimethyl ammonium chloride, and cetyl-dimethyl ethyl ammonium bromide. Exemplary monoalkyldimethylbenzyl ammonium salts include alkyldimethylbenzyl ammonium chlorides such as those sold under the names BTC 824, Hyamine 3500, Cyncal Type 14, and Catigene. Additionally included are substituted benzyl quaternary ammonium compounds including dodecyldimethyl-3, 4-dichlorobenzyl ammonium chloride such as that sold under the name Riseptin. Additionally included are mixtures of alkyldimethylbenzyl and alkyldimethyl substituted benzyl (ethylbenzyl) ammonium chlorides such as BTC 2125M, Barquat 4250. Dialkyldimethyl ammonium salts include didecyldimethyl ammonium halides such as those available as Deciquam 222 and Bardac 22, and octyldecyldimethyl ammonium chloride such as those available under the name DTC 812. Heteroaromatic ammonium salts include cetylpyridinium halide, the reaction product of hexamethylenetetramine with 1, 3-dichloropropene to provide cis-isomer 1-(3-chloroallyl)-3, 5, 7-triaza-1-azoniaadamantane, alkyl-isoquinolinium bromide, and alkyldimethyl-naphthylmethyl ammonium chloride. Poly substituted quaternary ammonium salts include alkyldimethylbenzyl ammonium saccarinate and methylethylbenzyl ammonium cyclohexylsulfamate. Bis-quatemary ammonium salts include 1, 10-bis(2-methyl-4-aminoquinolinium chloride)-decane and 1, 6-bis(1-methyl-3-(2, 2, 6-trimethyl cyclohexyl)-propyldimethyl ammonium chloride) hexane. Additionally included are polymeric quaternary ammonium compounds including those available under the names WSCP, Mirapol-A15, and Onamer M.
Exemplary quaternary phosphonium compounds include ethyltriphenyl phosphonium bromide, butyltriphenyl phosphonium chloride, methyltriphenyl phosphonium bromide, tetraphenyl phosphonium bromide, ethyltriphenyl phosphonium acetate, ethyltriphenyl phosphonium iodide, benzyltriphenyl phosphonium chloride, (ethoxycarbonylmethylene) triphenyl phosphorane, (ethoxycarbonylmethyl) triphenyl phosphonium bromide, (ethoxycarbonylmethyl) triphenyl phosphonium chloride, (formylmethylene) triphenyl phosphorane, (2-hydroxybenzoyl) methylenetriphenyl phosphorane, (2-hydroxyethyl) triphenyl phosphonium bromide, (2-hydroxyethyl) triphenyl phosphonium chloride, (methoxycarbonylmethyl) triphenyl phosphonium bromide, and (methoxycarbonylmethyl) triphenyl phosphonium chloride. A preferred quaternary compound includes tetrakishydroxymethyl phosphonium sulfate.
It should be appreciated that the above-identified quaternary compounds can be provided with other anions than those mentioned. Exemplary anions include chloride, sulfate, bromide, acetate, iodide, methyl ethyl sulfate.
The amount of antimicrobial agent is preferably provided in an amount that will reduce a bacterial concentration in the lubricant composition from greater than 105 (between 105 and 106) to less than 10 CFU/ml (colony forming units/ml) after two weeks. In the case of yeast and mold counts, the antimicrobial agents will preferably provide a reduction from an initial concentration of greater than 105 (between 105 and 106) to less than 10 CFU/ml within about one month. Another way of expressing a desired performance of the lubricant composition according to the invention is that it will preferably provide a two log reduction of bacteria in water in about two weeks, and a two log reduction of mold and yeast in water in about one month. Preferably, the lubricant composition will provide a four log in bacteria in about two weeks, and a four log reduction in mold and yeast in about one month. Most preferably, the lubricant composition will provide a five to six log reduction of bacteria in about two weeks, and a five to six log reduction in mold and yeast in about one month. Exemplary bacteria which can be reduced include Staphylococcus aureus, Escherichia coli, Enterobacter aerogenes, and Pseudomonas aeruginosa. Exemplary yeast and mold which can be reduced include Candida albicans, Saccharomyces cerevisiae, and Aspergillus niger. 
It is desirable for the antimicrobial agent to exhibit a distribution coefficient between water and oil phases of between about 0.1 and about 100. It is generally understood that the bacteria, yeast, or mold tends to grow in the water phase. That is, as water seeps into machinery including, for example, gear boxes, pumps, hydraulic systems, agitators, grinders, etc., bacteria, yeast, and/or mold may begin growing in the water phase. Accordingly, it is desirable for the antimicrobial agent to migrate from the oil phase into the water phase in order to kill the bacteria, yeast, or mold. The applicants discovered that by incorporating an microbial agent which is soluble in both oil and water into a lubricant composition, it is possible to kill the bacteria, yeast, or mold that tends to grow in the water phase. Furthermore, it is desirable to provide the antimicrobial agent so that it does not all transfer into the water phase. That is, it is desirable for the antimicrobial agent to partition between the oil phase and the water phase. This partitioning increases the longevity of the lubricant composition for killing bacteria, yeast, and mold. Preferably, the partition coefficient of the antimicrobial agent is preferably greater than 0.2 and more preferably greater than 0.5, and preferably less than 50 and more preferably less than 20.